Radio telegraph transmitter



Feb. 13, 1951 L. J. HEAToN-ARMSTRQN@ 25419955 RAIO TELEGRAPH TRANSMITTERFiled June 19;7 1947 lllvlll'llununulnlil.-

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ll'nuenmgW 7 Atlorne Patented Feb. 13, 1951 RADIO 'TELEGRAPH TRANSMTTERLouis John Heaton-Armstrong, London, England, assignor to International'Standard Electric Corporation, New York, N. Y., a. corporation ofDelaware Application June 19, 1947, `Serial No. 755,698 .InGreat BritainJune 18, 1946 Section 1, Public Law 690, August 8, 1946 'Patent expiresJune "18, 1966 5 Claims.

The present invention relates to the remote -control of radio telegraphtransmitters.

The principal object of the invention is to provide simple means forremotely and :selectively switching on and keying one or more radiotelegraph transmitters over .a circuit common to all the transmitters.

The invention provides a remote-control system for a telegraphtransmitter, comprising at the control location an oscillator, means forswitching the oscillator output on or off, means for keying thefrequency of the oscillator to give marking and spacing waves of.different frequencies, means for transmitting the output wave of thesaid oscillator to the transmitter location, and at the transmitterlocation means responsive to the amplitude of the oscillator wave forswitching on or oil the operating power for the transmitter, and meansresponsive to the `frequency of the oscillator wave for keying fthetransmitter.

The accompanying drawing gives 'a schematic circuit diagram of anembodiment of the invention. At the controlling station `there are threeoscillators I, 2, 3 having respective controlling telegraph keys 2i, 5and 6 arranged so that when any key is open, the correspondingoscillator delivers a certain frequency characterising a mark signal,and when the key is closed it delivers a different frequencycharacterising a space signal.

The oscillators are all connected to a two-conf ductor line l, v3 byrespective transformers 9, I@ and `I l, `the secondary windings of whichmay be connected in series as shown, or in parallel. Each oscillatorgenerates a different pair `oi frequencies, which for illustration aretaken as 300 and `350 cycles for oscillator I, `500 and 600 cycles foroscillator 2 and `1200 and 1400 cycles `for oscillator 3, the lowerfrequency in each case characterising the mark signal.

At the controlled station are three similar transmitterrcontrol circuitsI2, I3 and I 4, the details of No. I2 .only being given. The circuit ,l2 comprises two transformers I5 and I 6 .having primary windings tunedby condensers Il and I8 and connected in series between terminals I9 and20. The secondary windings of these transformers are connected to theinput diagonal terminals of individual bridge rectiiiers 2i and 22 inthe manner shown, the arrangement being such that the left-hand outputdiagonal terminal is positive to the right-hand terminal in both cases,when alternating current is supplied through the correspondingtransformers.

A neutral relay 23 has two .similar windings 2 connected in Opposition,each to the output terminals of one of the bridge rectiers, `in ,such.manner that if equal alternating voltages .are applied to both bridgerectiers, the relay would jbe substantially unaffected. The contacts Vofthe relay `are connected by .any suitable means (not shown) to controlapparatus for switching on the power for the radio transmitter served bythe control circuit rI 2.

The .positive output terminals of the two `bridge `rectiiiers il and 22are also connected respectively to the control grid and cathode of avalve `2li whose anode circuit is supplied with current from a hightension source (not shown) which should .be connected to .terminals 2.5and 2t, `a load resistance 2l being connected in series with the anode.

The output from the anode of the valve is obtained from terminal 28.connected tothe anode through a blocking condenser 29. The voltageobtained at terminal 28 will be applied to key the corresponding radiotransmitter by application to a grid of the oscillating valve (notshown) or in any other convenient Way.

The other control circuits I3 Yand I 4 `are eX- actly similar to I 2except as regards the frequency to which the transformers l5 and I6 aretuned. This will be explained later. The three Acontrol circuits areconnected in series to the line conductors l' and E, as indicated.

Assuming that the control circuit I2 corresponds to the oscillator i,the transformers I 5 and 'I 6 will be tuned respectively to the mark andspace frequencies 3G@ and 350 cycles. Initially, the oscillator I Vwillbe supposed to supply no current to the line through the transformer 3.No current being received hy either of the transformers I5 or I 6 in thecontrol circuit I2, the relay 23 will `not be operated, and thecorresponding radio transmitter will be switched off. When it is.desired to switch on the radio transmitter, the oscillator I isconnected to supply alternating current Vto the line l, S through thetransformer 9, by any suitable switching means (not shown). Suchswitching means may, for example, switch on .the power for operating theoscillator, or alternatively it may simply connect the transformer 9 tothe output circuit of the oscillator. If the telegraph key l is in theopen position shown, the marking frequency current of 300 cycles will be:applied lto the line, and will set up oscillating currents ci thisfrequency in the primary circuit of the tuned transformer I?, but willbe relatively unaiiected by the other transformer I6, .so that fromtransformer I t.

tive potential from the rectifier bridge 2| and Y a low negativepotential from the rectifier bridge 22, so that it will be positive withrespect to the cathode. A large anode currentl flows in the valve 24, sothat a low marking voltage will be obtained at terminal 28.

If now the key l is closed to send a spacing signal, the oscillatorfrequency is changed to 350 cycles, and the line current will nowenergize the transformer it and pass ineifectively through the primarycircuit of transformer l5. The relay 23 remains operated, the current inthe lower winding now preponderating over that in the upper winding, butthe control grid of the valve 24 will now be negative to the cathode,since the negative with respect to voltage generated by the rectifier 22will be greater than the positive voltage generated by the rectifier 2l. The anode current of the valve 2li will therefore be reduced orcompletely cut off, and the voltage at terminal `28 therefore rises to ahigh spacing value.

The relay 23 should preferably be of the slowto-release type so that itwill not be liable to be released at the moment when the frequency ofthe oscillator l is changed. It willbe evident that if the oscillator ibe switched off or disconnected the relay 23 will be released, and thecorresponding transmitter will be switched olf.

The control circuits i3 and it will have their transformers I5 and i5respectively tuned to the marking and spacing frequencies supplied bythe corresponding oscillators 2 and 3. These frequencies will be 500cycles and 600 cycles for circuit i and 1'200 cycles and 1400 cycles forcircuit l. They will both evidently operate in the same way as circuiti2.

It should be noted, however, that should, for example, oscillator 2 beswitched on instead of oscillator i, the current at 500 or SUG cyclesre- Yand nearly equal currents, the net effect of which will beinsufhcient to affect the relay of the latter if suitably chosen andadjusted. Thus the circuit l2 will not be effected by the switching onof either of the other circuits i3 and It, and vice versa. lt is to benoted also, that if one of the other circuits is switched onsimultaneously with circuit i2, the cross-lire voltages applied to thecontrol grid of the valve 2t and resulting from the small residualcurrents which will be respectively passed by the transformers l5 and I6will be small, nearly equal, and opposite, so that the resultingcross-fire will be a second order effect.

By using frequency-shift keying at the control station, the selectivecircuits represented by the tuned transformers l5 and I6 can be verysimple. Thus suppose the value of Q (ratio of reactance to resistance)of the tuned circuits is only 12, and that when the marking frequency of300 cycles is transmitted, +30 volts is obtained from transformer i5,then about l0 volts will be obtained The net voltage applied to operatethe relay and valve will than be +20 volts. When the spacing frequencyis sent, this net voltage will be reversed. It will usually bepreferable to arrange so that the valve is taken beyond saturation bythe application of the posi- Vmeans in series'.

4 V tive marking voltage, and beyond cut off by the negative spacingvoltage.

If instead the adjacent circuit I3 is operated. and a marking current of500 cycles is transmitted, the voltage produced by transformer i5 willbe about 2.5 volts and that produced by transformer I6 will be about 3.7volts and the difference,"namely 1.2 volts will be small enough inVcomparison with the normal operating voltage of 20 volts for thecross-fire to be negligible. The relay 23 can also very easily bedesigned to operate on a net voltage of 2O but not on a net voltage of1.2.

The partic-ularnumerical figures which have been given for illustrationare not essential to the invention, and' may be varied in any desiredway. Any desired number of transmitters may becontrolled in this mannerover a single circuit, Vthe only proviso being that different markingand spacing frequencies be selected for each transmittet 'Generallyspeaking, the closer these frequencies are chosen in relation to thedifference of the mean frequencies corresponding to adjacenttransimtter, the smaller will be the interference between them.

It may benoted that the arrangement of the transformers l5 and I6, therectiers 2l and 22 and the relay 23 is substantially the same as that-shown in Fig.2 of British patent specication No- 442,342, and itoperates on similar principles.

It will be noted that the operation of the neutral relay 23 isdetermined by the presence or absence of the Vcurrent coming from theoscillator l, that is upon its amplitude, and not by its frequency,while the operation ofthe valve 24 for keying the transmitter depends onthe frequency Yof the current.

What is claimed is:

1. A remote-control system forV a telegraph transmitter, comprisingoscillator means for producing a rst and a second frequency, atransmission line, control means for applying said frequenciesalternately to said transmission line, a

. rst and a second selective circuit serially connected across saidline, said circuits being electrically tuned to resonate at said firstand second frequency, respectively, load impedance means in each of saidcircuits connected to develop a maximum output lat the resonantfrequency of the respective circuit, a non-polar responsive device,circuit meansconnecting said load impedance means differentiallyto saiddevice so that the latter will be actuated when one of said outputsmaterially exceeds the other and will remain inactive when the twooutputs are substantially equal, a polar responsive device, circuitmeans connecting said load impedance means differentially across saidpolar responsive device so as to produce a rst and a second mode ofoperation of the latter device if a respective one of said outputsmaterially exceeds the other, and output means for controlling theoperation of a telegraph transmitter by the operation of both of saidresponsive devices.

2. The system'according to claim l wherein said non-polar devicecomprises a relay having two windings, said windings being connectedacross respective ones of said load impedance means, and wherein saidpolar device comprises an electronic discharge tube having an inputcircuit connected across both of said load impedance 3.' The systemaccording to claim l wherein each of said load impedance means in eachofsaid selected circuits comprises respectively a tronic discharge tubehaving an anode and a,

cathode, said tube serially connected across said source, a second loadimpedance serially connected between said anode and said source, and acapacitance serially disposed between said anode and one of said outputterminals.

LOUIS JOHN HEATON-ARMSTRONG.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS- Number Name Date 1,635,779 Cartier July 12, 19271,678,973 Brown July 31, 1928 1,897,739 Stablein Feb. 14, 1933 2,150,241Nichols Mar. 14, 1939 2,198,901 Boswau Apr. 30, 1940

